It is known that joints should be formed in hardenable or settable compositions such as concrete pavements, floors and the like in order to prevent surface cracks resulting from expansion and contraction of the composition during setting and subsequently from temperature changes. One current practice in the art is to form such joints by inserting a joint-former or divider edgewise into the composition while it is in a plastic condition. The joint-former or divider may be, for example, a plastic extrusion which is T-shaped in cross-section with the bar of the T being connected to the body of the T by a frangible connection. The lower section or web which forms the body is inserted vertically downward into the settable material to a level such that upper section or web forming the bar of the T engages the surface of the settable material. Thereafter, the upper section is stripped away from the embedded lower section, breaking the frangible connection and leaving the lower section in place so as to define a line of weakness along which cleavage or fracture of the mass due to shrinkage or settling is more apt to occur than on either side of the line. The stripped-away upper section, that is the section which is used to implant the lower section, is discarded. Such a system is described in U.S. Pat. No. 3,352,217.
Another two-piece joint-former of generally T-shaped cross-section is described in U.S. Pat. No. 4,090,800. In that system the implanting upper section is itself a unitary T-shaped section having a body portion which frictionally engages in a groove in the upper edge of the lower section. After implanting of the lower section the implanting section is removed. A somewhat analogous system is described in U.S. Pat. No. 3,838,930.
Each of the systems summarized above utilizes upper and lower sections which are dissimilar. That is, the implanting or upper section is different in shape from the implanted or lower section. In the system of U.S. Pat. No. 4,090,800 the implanting section is discarded after having been stripped away from the implanted section. This represents an added cost and also presents a trash removal problem in the case of a large concrete pouring project. In the system of U.S. Pat. No. 3,838,930 the upper section which is removed from the implanted lower section is reuseable with another piece of lower section, but the fact that the shapes of the upper and lower sections are different means that supplies of both types of sections must be provided at the construction site.